While I have no love for Pakistan, (Personally, I think it should have never been carved out in the first place after WW2.) I do not see much point in anything like Operation Pakistani Freedom or whatever. The invasion part is not going to be the troublesome part for big guys like the US or India. Instead, what to do afterwards? Bear in mind that Pakistan is an even more complicated mess than places like Iraq or Afghanistan.
Now then, let's just say that we invade Pakistan. How to pacify that place? Too many ethnic groups coupled with religious mess, topped by miserable local politics. (Plenty of political games involving the Indian boogie man, but not a whole lot of political will to clean up Pakistan!) You have to simplify: Pick one faction at the expense of everyone else. Proceed to run series of pest control over the others. Genocide? Yes, indeed, but that would be something I would consider as a post-invasion option if I were in charge of invading Pakistan. Also, if the last thing you want is to deal with intractable local politics, then you do have to consider hosing down lots of people. After all, you do not have to worry about proper governance over dead people.